Brakes have been relined and bled. New master cylinder and powerbooster. I have checked the vacuum to the powerbooster and it registers 50 lbs. Pull vacuum on booster and it holds vacuum, until pedal is depressed. When I pulled a vacuum on the booster, manually, brake holds. Turn on engine and there does not appear to be any booster as the peddle drops. Any ideas?

Turned out to be a bad master cylinder. Got two bad rebuilt master cylinders from parts place. Got a new one (not rebuilt) and the brakes are great. The vacuum valve is OK. Thanks for input.Turned out to be a bad master cylinder. Got two bad rebuilt master cylinders from parts place. Got a new one (not rebuilt) and the brakes are great. The vacuum valve is OK. Thanks for input.

1 Suggested Answer

Hi,
a 6ya expert can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
the service is completely free and covers almost anything you can think of.(from cars to computers, handyman, and even drones)
click here to download the app (for users in the US for now) and get all the help you need.Goodluck!

Tell us some more! Your answer needs to include more details to help people.You can't post answers that contain an email address.Please enter a valid email address.The email address entered is already associated to an account.Login to postPlease use English characters only.

Related Questions:

I know that when the engine is shut off, after one or two pumps you lose the power on brakes. Your problem has something to do with the engine vacuum that works in coordination with the master cylinder. Check out the vacuum system and/or connections involved.

was it a new master cylinder or a old one?' under the master cylinder is a load sensing equalising valve its a 136 euros piece of spare part new is this ok or was that damaged in the accident ,iam going to bed had a late night on a breakdown last night and then up early so iam a bit tired to think straight sorry

Are you losing any Brake Fluid? Is it visible anywhere at the four wheels? Is it visible anywhere else?
The Master Cylinder may be defective. When you bled the Brakes did you maintain proper Brake Fluid Level in the Master Cylinder? If you didn't: and air entered into the Master Cylinder there maybe air within in the system in the Master Cylinder. You can bleed the Master Cylinder by removing the brake lines, adding more fluid, pumping the brakes, bleeding the air out of the system.
Are you losing Brake Fluid and can't find a noticeable leak? Then there is a good posibility that the rear seal in the Master Cylinder is leaking and the Fluid is going into the Brake Booster - which is the large wheel shaped drum located on the fire wall. In this case both the Brake Booster and the Master Cylinder will have to be removed and replaced. The Booster contains seals that Brake Fluid is very caustic to and will ruin these seals- causing future failures.
If no Brake Fluid is lost, no leak found: Check the Brake Booster Vacuum Advance. This should be connected to the outside of the Booster, attached to a hose, with the hose going to the engine. Check to see if this is working properly. Replace if needed.

Did you bench bleed the master cyl. before installing it? then when you installed the new master, did you bleed all 4 points? If yes, then check all for points for leaking caliper/s and leaking wheel cylinder/s. If the van has ABS, check the valve body for a bleeder screw and see if air bleeds out of it. If you've checked everything twice and did everything right then your new master cyl. may be defective.